First identified by molecular cloning in 1989 (Choo, et al., Science 244: 359-362 (1989)), hepatitis C virus (HCV) is now widely accepted as the most common causative agent of post-transfusion non A, non-B hepatitis (NANBH) (Kuo, et al., Proc. Natl. Acad. Sci. USA 87: 2057-2061 (1989)). Infection with HCV is a major cause of human liver disease throughout the world with seroprevalence in the general population ranging from 0.3 to 2.2% (van der Poel, et al., In Reesink, H. W., ed. HEPATITIS C VIRUS, Amsterdam:Karger; p. 137-163 (1994)) to as high as .about.10-20% in Egypt (Hibbs, et al., J. Infect. Dis. 168:789-790 (1993)). Although the virus is most commonly transmitted via blood, the mode of transmission remains unknown for a large portion of infected individuals (Alter, et al., Infect. Agents Dis. 2: 155-166 (1993)). Over 50% of infections by HCV progress to acute hepatitis associated with viremia and generally elevated serum alanine aminotranferase (ALT) levels (Alter, H. J., CURRENT PROSPECTIVE IN HEPATOLOGY, New York: Plenum p. 83-97 (1989)). Over half of the acute cases progress to a chronic infection with roughly 20% developing cirrhosis (Alter, H. J., CURRENT PROSPECTIVE IN HEPATOLOGY, New York: Plenum p. 83-97 (1989)). Chronic infection by HCV has also been linked epidemiologically to the development of hepatocellular carcinoma (HCC), especially in cirrhotic patients (Blum, et al., Hepatology. 19: 251-258 (1994)).
Since its initial identification, many isolates of HCV have been sequenced, displaying much genetic diversity and leading to the subclassification of this virus into multiple genotypes (Bukh, et al., Proc. Natl. Acad. Sci. USA 90: 8234-8238 (1993); Bukh, et al., Proc. Natl. Acad. Sci. USA 91: 8239-8243 (1994); Dusheiko, et al., Hepatology 19:13-18 (1994)). Due to its genome structure and sequence homology, this virus was assigned as a new genus in the Flaviviridae family, along with the other two genera, flaviviruses (such as yellow fever virus and Dengue virus types 1-4) and pestiviruses (such as bovine viral diarrhea virus) (Choo, et al., Science 244: 359-362 (1989); Miller, et al., Proc. Natl. Acad. Sci. USA 87: 2057-2061 (1990)). Like the other members of the Flaviviridae family, HCV is an enveloped virus containing a single-stranded RNA molecule of positive polarity. The HCV genome is approximately 9.6 kilobases (kb) with a long, highly conserved, noncapped 5' nontranslated region (NTR) of approximately 340 bases which functions as an internal ribosome entry site (IRES) (Wang, et al., Curr. Topics Microbiol. Immunol. 203: 99-115 (1995)). This element is followed by a region which encodes a single long open reading frame (ORF) encoding a polypeptide of .about.3000 amino acids comprising both the structural and nonstructural viral proteins. This large polypeptide is subsequently processed into the individual structural and nonstructural proteins by a combination of host and virally-encoded proteinases (reviewed in Rice, B. N. Fields, D. M. Knipe, and P. M. Howley (eds.), VIROLOGY, 2d ed., p. 931-960, Raven Press, New York (1996)).
Although a robust culture system for propagating HCV has not yet been reported, the putative functions of the viral gene products were initially predicted by their homology to the viral proteins found in other members of the Flaviviridae family, whose functions were known. Many of these predictions were later demonstrated experimentally for the individual HCV proteins using recombinantly expressed proteins (reviewed in Rice, B. N. Fields, D. M. Knipe, and P. M. Howley (eds.), VIROLOGY, 2d ed., p. 931-960, Raven Press, New York (1996)). However, the function of HCV NS4B protein, like that of the NS4B in the other members of the Flaviviridae family, is still unknown.
Inhibition of ATPase proteins of the Flaviviridae family, particularly HCV NS4B protein, is potentially of benefit in controlling, reducing and alleviating the diseases caused by infection with these organisms. There remains a need for treatment, in this field, for compounds which are capable of inhibiting or activating these proteins, in particular HCV NS4B protein.